A robotic, compact, and extremely high resolution optical spectrograph for a close-in super-Earth survey

摘要

One of the most astonishing results from the HARPS and Kepler planet surveys is the recent discovery of close-in super-Earths orbiting more than half of FGKM dwarfs. This new population of exoplanets represents the most dominant class of planetary systems known to date, is totally unpredicted by the classical core-accretion disk planet formation model. High cadence and high precision Doppler spectroscopy is the key to characterize properties of this new population and constrain planet formation models. A new robotic, compact high resolution optical spectrograph, called TOU (formerly called EXPERT-III), was commissioned at the Automatic Spectroscopic Telescope (AST) at Fairborn Observatory in Arizona in July 2013 and has produced a spectral resolution of about 100,000 and simultaneous wavelength coverage of 0.38-0.9 μm with a 4kx4k back-illuminated Fairchild CCD detector. The instrument holds a very high vacuum of 1 micro torr and about 2 mK temperature stability over a month. The early on-sky RV measurements show that this instrument is approaching a Doppler precision of 1 m/s (rms) for bright reference stars (such as Tau Ceti) with 5 min exposures and better than 3 m/s (P-V, RMS~1 m/s) daily RV stability before calibration exposures are applied. A pilot survey of 20 V<9 FGK dwarfs, including known super-Earth systems and known RV stable stars, is being launched and every star will be observed ~100 times over ~300 days time window between this summer and next spring, following up with a full survey of ~150 V< 10 FGKM dwarfs in 2015-2017.